A vehicle with an engine may include an evaporative emission control system coupled to a fuel system in order to reduce fuel vapor emissions. For example, an evaporative emission control system may include a fuel vapor canister coupled to a fuel tank which includes a fuel vapor adsorbent for capturing fuel vapors from the fuel tank while providing ventilation of the fuel tank to the atmosphere.
Leak testing may be periodically performed on such evaporative emission control systems in order to identify leaks in the system so that maintenance may be performed and mitigating actions may be taken in order to reduce emissions. In some examples, natural vacuum approaches may be used to perform leak detection in evaporative emissions systems in vehicles, e.g., in hybrid electric vehicles. Such approaches may use current-drawing devices, e.g., electro-mechanical valves, in order to seal off the fuel system in order to perform leak diagnostics.
The inventors herein have recognized that in approaches which use current-drawing devices to seal the evaporative system, the power consumption associated with actuating the current-drawing devices to seal the evaporative system may be disadvantageous. For example, such current-drawing devices may draw a significant amount of current to seal off and maintain sealed the evaporative system during leak testing. This power consumption may reduce the time the test can execute during engine off conditions, e.g., after a key off event. Further, this energy draw may reduce how long the evaporative test can execute during engine off conditions in applications where battery power is limited, e.g., in hybrid electric applications. Furthermore, in engine application with limited engine run time, e.g., in hybrid electric vehicles, sufficient natural vacuum may not be available for leak testing while the engine is running.
In one example approach, in order to at least partially address these issues, a method for a vehicle with an engine comprises generating engine off vacuum or pressure in a fuel system for leak diagnostics, where the pressure and vacuum are held via first and second mechanical relief valves positioned in parallel with one another and without a valve holding current.
In this way, passive valves may be used to seal the evaporative system during engine off conditions without utilizing current-drawing devices and the naturally occurring diurnal temperature cycle may be used to generate engine off vacuum or pressure in the fuel system for leak diagnostics. Further, by using passive valves, an engine controller can stay alive for hours or even may wake up later to perform leak analysis since power is not consumed by the passive valves. Such an approach may provide greater flexibility and reduce costs associated with leak testing in an evaporative emission control system especially in hybrid electric systems where active vacuum pumps are used.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.